A universal clamp assembly for receiving an electrical conductor having a variety of diameters without exchanging parts. An insulator includes a support fitting thereon. The clamp assembly includes a keeper fixed to an end of the fitting with two guide arms disposed along two sides thereof. An internally threaded bore in the keeper has a longitudinal axis. An externally threaded bolt is threadedly received in the bore. The assembly also includes a clamp member relatively rotatably receiving and axially restraining the bolt and located adjacent to the keeper for translational movement of the clamp member relative to the keeper along the longitudinal axis of the bolt. The clamp member includes two axially extending sliding arms adjacent the two guide arms. Rotation of the bolt along the longitudinal axis moves the clamp member towards and away from the keeper.